Floquet Engineering Achieves Control of Hubbard Excitons in Sr CuO

Key Takeaways

• Floquet engineering rotates Hubbard exciton states up to π/2.
• Third‑harmonic generation reveals coherent wavefunction manipulation.
• χ^(3) reaches ~1.4×10^7 pm^2/V^2 at resonance.
• Floquet sidebands confirm periodic driving of many‑body exciton.
• Platform enables ultrafast quantum control in correlated solids.

Pulse Analysis

Floquet engineering—periodic driving of quantum systems with non‑resonant light—has become a cornerstone of modern quantum materials research, but its application has largely been limited to weakly interacting electrons or simple lattice models. The recent demonstration in Sr₂CuO₃ pushes the technique into the realm of strongly correlated Mott insulators, where electron‑electron repulsion creates complex many‑body excitations. By treating the Hubbard exciton as a two‑level system, researchers bridge the gap between abstract Floquet theory and tangible control of emergent quasiparticles, opening a new experimental frontier.

The team employed intense mid‑infrared pulses to dress the excitonic wavefunction while monitoring the response with resonant third‑harmonic generation. The THG signal displayed a clear dependence on the rotation angle of the exciton, vanishing at a π rotation and producing sidebands spaced by the driving frequency—hallmarks of coherent Floquet dressing. Notably, the measured third‑order susceptibility reached 1.4 × 10⁷ pm² V⁻², a record for a solid‑state system, providing unprecedented sensitivity to the exciton’s parity mixing and confirming ultrafast Rabi‑like oscillations in a many‑body context.

Beyond fundamental physics, this level of control has immediate implications for quantum technologies. Programmable pulse sequences could tailor electronic band structures on demand, enabling photo‑induced superconductivity or topological transitions in correlated oxides. The pronounced nonlinear response also suggests a route to exciton‑based quantum sensors, where wavefunction rotations amplify sensitivity to charge, spin, or chemical potential variations. As the community moves toward terahertz driving and full SU(2) control, the platform demonstrated in Sr₂CuO₃ is poised to become a workhorse for ultrafast material design and next‑generation quantum devices.